RT8096A

Copyright © 2019 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8096A-06

December

2019

www.richtek.com

13

Application Information

The RT8096A is a single-phase step-down converter. It

provides single feedback loop, constant on-time current

mode control with fast transient response. An internal

0.6V reference allows the output voltage to be precisely

regulated for low output voltage applications. A fixed

switching frequency (1.5MHz) oscillator and internal

compensation are integrated to minimize external

component

count.

Protection

features

include

over-current protection, under-voltage protection and

over-temperature protection.

Output Voltage Setting

Connect a resistive voltage divider at the FB between

VOUT and GND to adjust the output voltage. The output

voltage is set according to the following equation :

OUT

REF

R1

V

= V

1

R2









where VREF is the feedback reference voltage 0.6V

(typ.).

FB

GND

VOUT

R1

R2

Figure 1. Setting VOUT with a Voltage Divider

Chip Enable and Disable

The EN pin allows for power sequencing between the

controller bias voltage and another voltage rail. The

RT8096A remains in shutdown if the EN pin is lower

than 400mV. When the EN pin rises above the VEN trip

point, the RT8096A begins a new initialization and

soft-start cycle.

Internal Soft-Start

The RT8096A provides an internal soft-start function to

prevent large inrush current and output voltage

overshoot when the converter starts up. The soft-start

(SS) automatically begins once the chip is enabled.

During soft-start, the internal

soft-start capacitor

becomes charged and generates a linear ramping up

voltage across the capacitor. This voltage clamps the

voltage at the FB pin, causing PWM pulse width to

increase slowly and in turn reduce the input surge

current. The internal 0.6V reference takes over the loop

control once the internal ramping-up voltage becomes

higher than 0.6V.

UVLO Protection

The RT8096A has input Under Voltage Lockout

protection (UVLO). If the input voltage exceeds the

UVLO rising threshold voltage (2.25V typ.), the

converter resets and prepares the PWM for operation.

If the input voltage falls below the UVLO falling

threshold voltage during normal operation, the device

will stop switching. The UVLO rising and falling

threshold

voltage

has

a

hysteresis

to

prevent

noise-caused reset.

Inductor Selection

The switching frequency (on-time) and operating point

(% ripple or LIR) determine the inductor value as

shown below :





OUT

IN

OUT

SW

LOAD(MAX)

IN

V

V

V

L =

f

LIR

I

V









where LIR is the ratio of the peak-to-peak ripple current

to the average inductor current.

Find a low loss inductor having the lowest possible DC

resistance that fits in the allotted dimensions. The core

must be large enough not to saturate at the peak

inductor current (IPEAK) :

PEAK

LOAD(MAX)

LOAD(MAX)

LIR

I

= I

+

I

2









The calculation above serves as a general reference.

To further improve transient response, the output

inductor can be further reduced. This relation should be

considered along with the selection of the output

capacitor.

Inductor saturation current should be chosen over IC’s

current limit.